A relay device achieved by modularizing plural relay units on a common wiring board (base plate) is used for a vehicle or the like, because many relays can be integrated within a small limited space. For example, U.S. Pat. No. 6,686,821B2 (JP-A-2002-343216) proposes a relay device, which uses a base plate as a wiring board. The based plate is provided by subjecting a lead-frame-shaped press-molding article using wiring metal pieces to insert resin molding. The end portions of these wiring metal pieces are bent and used as connection terminals.
Furthermore, JP-A-2000-83310 proposes a relay device in which a print board having an integrated circuit element (IC) mounted thereon is perpendicularly fixed to a base plate.
Recently, miniaturization of relay devices is more and more required, and the interval between the respective relay units in each relay device is narrowed. Therefore, coil heating caused by current supplied to respective coils affects adjacent relay units through this narrow interval or through wiring metal pieces of the base plate from the terminals.
It is difficult to radiate heat generated by the coils because each relay unit is surrounded by other relay units or the like. As a result, an increase in coil temperature substantially limits the miniaturization of the relay device. Furthermore, a power saving requirement to the relay device is more and more demanded year by year.
In order to solve this problem, it is considered that a coil-applied voltage is reduced after a contact point operation based on a current supply to coils has been completed, thereby reducing the heating of the coils. In this case, however, dispersion in the manufacturing of coils or an increase of temperature causes an increase of coil resistance. Thus, the coil-applied voltage (holding voltage) must be reduced in consideration of the increase of the coil resistance. As a result, for example, when current is supplied to only one relay unit or when the external temperature is low, and thus an increase of coil resistance is small, the holding voltage cannot be actually reduced although it is expected to be originally reduced to a lesser value.